Chapter 28: The Reproductive System

Transcription

1 Chapter 28: The Reproductive System Chapter Objectives MALE REPRODUCTIVE SYSTEM 1. List the major components of the male reproductive system and their general functions. 2. Explain the structure of the testes. 3. Explain the functions of the seminiferous tubules, sustentacular cells and interstitial cells. 4. Explain the structure and functions of the scrotum in its role of protection and temperature regulator. 5. List the structures found in the spermatic cord. 6. Explain the structure and functions of the penis. 7. List the parts of the autonomic nervous system that control erections and ejaculation. 8. Explain the structure and functions of the epididymis. 9. Explain the structure and functions of the ductus (vas) deferens. 10. Explain the structure and functions of the ejaculatory ducts. 11. Explain the structure and functions of the urethra. 12. Explain the structure and function of the seminal vesicles. 13. Explain the structure and function of the prostate gland. 14. Explain the structure and function of the bulbourethral gland. 15. Describe the origins as well as cellular and chemical characteristics of semen. 16. Define spermatogonia, primary spermatocyte, secondary spermatocyte, spermatid, and sperm. 17. Describe and explain the events of spermatogenesis and spermiogenesis. 18. Explain the difference between spermatogenesis, spermiogenesis and spermiation. 19. Discuss hormones that control the production of sperm, with emphasis on the actions of each type of hormone with the different types of cells in the testes. 20. Describe the structure of a mature sperm. FEMALE REPRODUCTIVE SYSTEM 21. Describe the general location and functions of the ovaries, uterine (Fallopian) tubes, uterus, vagina, vulva, and mammary glands. 22. Describe the external accessory structures that hold the ovaries in place. 23. Discuss the histology of the ovaries. 24. Describe the uterine tubes' general and epithelial structure, in addition to their operation in transport of the secondary oocyte after ovulation. 25. Identify the anatomical subdivisions of the uterus.

2 26. Discuss the three histological layers of the uterus. 27. Provide a detailed histological description of the endometrium. 28. Discuss the composition of the cervical mucosa and correlate the changes in the cervical mucosa to its effects on the sperm. 29. Name the anatomic structures of the vagina. 30. Differentiate the functions of the distinct external structure of the vulva: the Labia majora, Labia minora, Clitoris, and Bulb of Vestibule. 31. Describe the location, anatomy and function of the mammary glands. 32. Follow the steps of oogenesis. 33. Trace the formation and development of the ovarian follicles. 34. Relate the timing of oogenesis to follicle development. FEMALE REPRODUCTIVE CYCLE 35. Describe the difference between the uterine and ovarian cycles. 36. Discuss the hormones that control the female reproductive cycle. Describe each hormone s function. 37. Note the normal time span for each of the four phases of the female reproductive cycle. 38. Portray the events occurring with the follicles in the ovaries and the tissue changes in the endometrium during the menstrual phase. 39. Discuss the changes in hormone levels during the preovulatory phase 40. Discuss the changes in hormonal levels that initiate ovulation. 41. Explain the consistency of the postovulatory interval and course of development of the corpus luteum and endometrium depending on whether fertilization does or does not occur. Chapter Lecture Notes Introduction Male and female reproductive systems are a series of glands and tubes that produce and nurture sex cells, and transport them to the site of fertilization. Organs of the Male Reproductive System Testes primary sex organ of the male reproductive system (Fig 28.1, 28.3 & 28.4) Testes or testicles - ovoid glands (gonads) suspended by a spermatic cord in the scrotum Tunica Vaginalis

3 Piece of peritoneum that descended with testes into scrotal sac Facilitates movement of testes within scrotum Structure of the Testes Tunica Albuginea - dense white capsule on the outside lobules contain highly coiled seminiferous tubules and are separated by connective tissue Seminiferous tubules - lined with stratified epithelium that gives rise to sperm cells Sertoli cells or sustentacular cells large cells embedded among the spermatogenic cells in the seminiferous tubules blood-testis barrier - tight junctions between sustentacular cells prevent an immune response against the spermatogenic cells nourish spermatocytes, spermatids, and spermatozoa Organs of the Male Reproductive System mediate the effects of testosterone and follicle stimulating hormone on spermatogenesis phagocytose excess spermatids cytoplasm as development proceeds control movements of spermatogenic cells and the release of spermatozoa into the lumen of the seminiferous tubule secrete fluid for sperm transport secrete the hormone inhibin, which slows sperm production by inhibiting FSH Interstitial cells (Leydig cells) - produce the male hormones (testosterone) Channels leading from the seminiferous tubules carry sperm to the epididymis and ductus (vas) deferens Scrotum - a pouch of skin and subcutaneous tissue that houses the testes (Fig 28.1 & 28.2) Temperature regulation of testes sperm survival requires 3 degrees lower temperature than core body temperature skin contains dartos muscle which causes wrinkling

4 when warm, muscle is relaxed to increase surface area for cooling wrinkles when cold to conserve heat cremaster muscle in spermatic cord elevates testes on exposure to cold & during arousal warmth reverses the process Spermatic cord - a supporting structure of the male reproductive system, consisting of (Fig 28.2) cremaster muscle ductus (vas) deferens testicular artery veins and lymphatic vessels autonomic nerves Penis - contains the urethra and is a passageway for the ejaculation of semen (Fig 28.10) Four anatomical parts root bulb crura (pl), crus (s) body glans penis Body contains three erectile tissue masses paired corpora cavernosa penis (1 & 2) unpaired corpus spongiosum penis (3) filled with blood sinuses lined by endothelial cells surrounded by smooth muscle and elastic connective tissue Erection parasympathetic reflex causes erection

5 sexual stimulation dilation of arteries supplying the penis nitric oxide mediates local vasodilation erectile dysfunction drugs increase vasodilation veins become compressed, and blood is trapped Ejaculation sympathetic reflex muscle contractions close sphincter at base of bladder peristaltic contractions in the vas deferens, seminal vesicles, ejaculatory ducts and prostate propel semen into the penile portion of the spongy urethra blood flow is restricted to penis and small muscles around the erectile tissue masses forces blood out of the penis and the penis will become flaccid again Male Duct System Epididymis - a tightly coiled tube lying adjacent to the testis and leading from the testis to the vas deferens (Fig 28.3) Site of sperm maturation and storage sperm may remain in storage here for at least a month, after which they are either expelled or degenerated and reabsorbed Ductus (Vas) Deferens (seminal duct) a muscular tube 45 centimeters in length leading from the epididymus up into the body cavity (Fig 28.1 & 28.3) unites with the ejaculatory duct and empties its contents into the urethra lined with pseudostratified columnar epithelium & covered with heavy coating of muscle conveys sperm along through peristaltic contractions Ejaculatory duct - union of the ducts from the seminal vesicles and ductus deferens (Fig 28.1) function to eject spermatozoa into the prostatic urethra Male urethra - shared terminal duct of the reproductive and urinary systems (Fig 28.1) serves as a passageway for semen and urine

6 male urethra is subdivided into three portions: Prostatic urethra (through prostate gland) Intermediate urethra (through deep muscles of perineum) Penile (spongy) urethra (through corpus spongiosum) Accessory Sex Glands Seminal Vesicle - a saclike structure attached to the vas deferens near the base of the urinary bladder (Fig 28.1 & 28.9) secretes a alkaline fluid that neutralizes acid in the male urethra and female reproductive tract fluid also contains fructose - nourishes sperm prostaglandins - cause muscular contractions in the female tract to help propel sperm to the egg cell semenogelin - causes coagulation of semen after ejaculation Prostate Gland - a chestnut-shaped structure surrounding the urethra at the base of the urinary bladder (Fig 28.1 & 28.9) secretes a milky, slightly acidic fluid that contains: citric acid, which can be used by sperm for ATP production acid phosphatase enzymes prostate-specific antigen (PSA) pepsinogen lysozyme amylase hyaluronidase - liquefies coagulated semen

7 Bulbourethral (Cowper s) Glands - small structures located inferior to the prostate (Fig 28.1 & 28.9) secrete mucus to lubricate the tip of the penis during sexual arousal secrete an alkaline substance that neutralizes acid Semen - a combination of sperm cells and the secretions of the seminal vesicles, prostate gland, and bulbourethral glands 120 million sperm/milliliter of semen Spermatogenesis Spermatogenesis sperm production (Fig 28.4 & 28.5) Spermatogonia undifferentiated spermatogenic cells that contain 46 chromosomes spermatogonia enlarge, undergo mitosis and become primary spermatocytes Primary spermatocytes spermatogenic cells that are in Meiosis I and still have 46 chromosomes complete first meiotic division to become secondary spermatocyte Secondary spermatocytes - spermatogenic cells that are in Meiosis II and are haploid with 23 chromosomes complete second meiotic division to become spermatids Spermatids four haploid cells produced from one primary spermatocyte Spermiogenesis - maturation of the spermatids into sperm the final stage of spermatogenesis Spermiation - the release of a sperm from its connection to a Sertoli cell Hormonal Control of Spermatogenesis (Fig 28.7) Puberty hypothalamus increases its stimulation of anterior pituitary by secreting GnRH anterior pituitary increases secretion LH & FSH LH stimulates Leydig cells to secrete testosterone

8 an enzyme in prostate & seminal vesicles converts testosterone into dihydrotestosterone (DHT is more potent) FSH stimulates spermatogenesis with testosterone, stimulates Sertoli cells to secrete androgen-binding protein (keeps hormones levels high) Testosterone (Fig 28.8) stimulates final steps spermatogenesis controls the growth, development, functioning, and maintenance of sex organs stimulates bone growth, protein anabolism, and sperm maturation stimulates development of male secondary sex characteristics Negative feedback systems regulate testosterone production Inhibin - produced by Sertoli cells Inhibits secretion of FSH helps to regulate the rate of spermatogenesis decreases sperm production when sperm production is sufficient when sperm production is proceeding too slowly less inhibin is released by the Sertoli cells, more FSH will be secreted and sperm production will be increased Sperm morphology (shape) (Fig 28.6) head contains DNA acrosome cap on the head which contains hyaluronidase and proteinase enzymes midpiece contains mitochondria to form ATP tail is flagellum used for locomotion produced at the rate of about 300 million per day once ejaculated sperm have a life expectancy of 48 hours within the female reproductive tract Organs of the Female Reproductive System

9 Ovaries - primary sex organ of the female reproductive system (Figs 28.11, & 28.16) Ovaries - solid, ovoid structures located within the lateral pelvic cavity maintained in position by a series of ligaments Broad ligament suspends uterus from side wall of pelvis Mesovarium attaches ovaries to broad ligament Ovarian ligament anchors ovary to uterus Suspensory ligament covers blood vessels to ovaries Round ligament attaches uterus to inguinal canal Ovary Structure (Fig 28.13) Germinal epithelium simple cuboidal epithelium that covers the surface of the ovary but does not give rise to ova Tunica albuginea dense irregular connective tissue Ovarian cortex - contains ovarian follicles Ovarian medulla - contains blood vessels, lymphatics, and nerves Female Internal Accessory Organs Uterine Tubes (oviducts, Fallopian tubes) - suspended by the broad ligament and lead to the uterus (Fig & 28.17) infundibulum funnel shaped portion near each ovary fimbrae fringe of finger-like projections cells lining the tubes have cilia, which beat in unison, drawing the egg cell into the uterine tube Uterus (Fig 28.16) Gross anatomy fundus dome shaped portion superior to uterine tubes body central portion of uterus isthmus constricted portion of uterus between body and cervix

10 cervix inferior portion that opens to vagina Histology Endometrium simple columnar epithelium lamina propria of connective tissue with uterine (endometrial) glands penetrating into layer stratum functionalis superficial layers of endometrium that are shed during menstruation stratum basalis deep layer of endometrium that replaces stratum functionalis each month Myometrium 3 layers of smooth muscle Perimetrium visceral peritoneum Cervical mucus - a mixture of water, glycoprotein, serum-type proteins, lipids, enzymes, and inorganic salts produced by the secretory cells of the mucosa of the cervix when thin, is more receptive to sperm when thick, forms a cervical plug that physically impedes sperm penetration mucus supplements the energy needs of the sperm serves as a sperm reservoir which protects the sperm from the hostile environment of the vagina, and protects sperm from phagocytes Vagina - a fibromuscular tube that extends from the uterus to the outside (Fig 28.20) Histology - three layers mucosal layer stratified squamous epithelium & areolar connective tissue

11 large stores of glycogen breakdown to produce acidic ph which set up a hostile acid environment for sperm muscularis layer - smooth muscle allows for considerable stretch adventitia - areolar connective tissue that binds it to other organs Female External Reproductive Organs Vulva (pudendum) - external genitalia of the female (Fig 28.20) Labia majora (labium major) - enclose and protect the other external reproductive organs correspond to the scrotum of the male Labia minora (labium minus) - flattened, longitudinal folds between the labia majora that form a hood around the clitoris Many blood vessels cause the labia minora to appear pink corresponds to the spongy urethra of the male Clitoris - a mass of erectile tissue at the anterior end of the vulva between the labia minora corresponds to the penis Vestibule - a space enclosed by the labia minora into which the vagina opens posteriorly corresponds to the membranous urethra of the male A pair of vestibular glands lie on either side of the vaginal opening; these correspond to bulbourethral glands Mammary Glands Mammary glands - modified sudoriferous (sweat) glands that lie over the pectoralis major and serratus anterior muscles (Fig 28.22) alveoli - milk-secreting cells that are clustered in lobules within the breasts Functions of the mammary glands synthesis of milk lactation - secretion and ejection of milk Follicular Development

12 Oogenesis egg cell development (Fig & Table 28.1) Germ cells migrate to ovary & become oogonia Oogonia female diploid stem cells that divide by mitosis to produce millions of oocytes in the female fetus Atresia process by which most germ cells degenerate before birth Primary oocyte stem cell that has entered Meiosis I and stops in Prophase I process halts and does not resume until puberty 200,000 to 2 million are present at birth 40,000 remain at puberty, but only 400 mature during a woman s life Secondary oocyte haploid stem cell that continues Meiosis and stops at Metaphase II produced starting at puberty monthly hormonal changes trigger maturation Penetration by the sperm causes the final stages of meiosis to occur Follicle Maturation (Fig & Table 28.1) Ovarian follicles - oocytes and support cells in various stages of development Primordial follicle - a primary oocyte surrounded by a single layer of squamous follicular cells formed during prenatal development Primary follicle - a primary oocyte surrounded by cuboidal follicular cells form at puberty the follicle enlarges and the follicular cells proliferate into granulosa cells and theca cells zona pellucida glycoprotein layer around primary oocyte corona radiata single layer of follicular cells attached to the zona pellucida Secondary follicle a follicle that has a fluid-filled cavity (antrum) Mature follicle - contains a secondary oocyte and a large antrum Ovulation release of the secondary oocyte from the surface of the ovary (Fig 28.13)

13 cumulus oophorus follicular cells outside of the corona radiata that leave the ovary with the ovulated secondary oocyte If the secondary oocyte is not fertilized shortly after its release, it will degenerate Corpus hemorrhagicum ruptured follicle Corpus luteum reorganized follicle after ovulation that is yellow in color fills in with hormone-secreting cells Corpus albicans - white scar left after corpus luteum regresses Female Reproductive Cycle Ovarian cycle changes in ovary during & after maturation of oocyte Uterine (menstrual) cycle involves changes in the endometrium preparation of uterus to receive fertilized ovum if implantation does not occur, the stratum functionalis is shed during menstruation Cyclical changes in the breasts and the cervix Hormonal Regulation of the Female Reproductive Cycle GnRH controls the female reproductive cycle (Fig 28.23) stimulates the release of FSH and LH FSH initiates growth of follicles that secrete estrogen and inhibin LH stimulates ovulation & promotes formation of the corpus luteum which secretes estrogens, progesterone, relaxin & inhibin Estrogen maintains reproductive organs promotes secondary sex characteristics and the breasts prepares the endometrium for implantation prepares the mammary glands for milk synthesis

14 inhibits the release of GnRH and secretion of LH and FSH Progesterone prepares uterus for implantation prepares the mammary glands for milk synthesis Relaxin relaxes the uterus for implantation Inhibin inhibits the secretion of FSH Phases of the Female Reproductive Cycle The female reproductive cycle may be divided into four phases (Fig & 28.26) Menstrual cycle (menstruation) - lasts for approximately the first 5 days of the cycle In the ovary several follicles begin to develop into secondary follicles In the uterus the stratum functionalis layer of the endometrium is shed, discharging blood, tissue fluid, mucus, and epithelial cells Preovulatory Phase - days 6-13 In the ovary (follicular phase) the secondary follicles increase their estrogen and inhibin production inhibin slows the secretion of FSH increasing estrogen increases the secretion of LH a dominant follicle continues to develop into a mature ovarian (Graafian) follicle by day 14, the Graafian follicle has enlarged & bulges at surface of the ovary In the uterus (proliferative phase) endometrial repair occurs this time between menstruation and ovulation is more variable in length that the other phases Ovulation usually occurs on day 14 in a 28-day cycle (Fig 28.25)

15 high levels of estrogen during the last part of the pre-ovulatory phase exert positive feedback on both LH and GnRH to cause ovulation FSH levels depressed by increase in inhibin a LH surge brings about the ovulation Following ovulation, the vesicular ovarian follicle collapses to become the corpus hemorrhagicum and reorganizes to become the corpus luteum Stimulated by LH, the corpus luteum secretes estrogens, progesterone, relaxin and inhibin Postovulatory - days Time between ovulation and onset of the next menstrual period Most constant timeline = lasts 14 days In the ovary (luteal phase) both estrogen and progesterone are secreted in large quantities by the corpus luteum if fertilization does not occur, then the corpus albicans is formed as estrogen and progesterone levels drop, secretion of GnRH, FSH & LH rise if fertilization does occur, then the developing embryo secretes human chorionic gonadotropin (hcg) which maintains health of corpus luteum & its hormone secretions In the uterus (secretory phase) hormones from corpus luteum promote thickening of endometrium to mm formation of more endometrial glands & vascularization if no fertilization occurs, menstrual phase will begin